Three Mile Island Unit 1

Three Mile Island Unit 1
Name	Three Mile Island Unit 1
Country	United States
Location	Dauphin County, Pennsylvania
Coordinates	40°10′44″N 76°43′06″W
Status	Decommissioned
Operator	Met-Ed / GPU / AmerGen / Exelon
Construction started	1968
Commissioned	1974
Decommissioned	2019
Reactor type	PWR
Reactor supplier	Babcock & Wilcox
Thermal capacity	2630 MWt
Electrical capacity	819 MWe
Cooling source	Susquehanna River

Three Mile Island Unit 1 Three Mile Island Unit 1 was a commercial pressurized water reactor electrical generating unit located on Three Mile Island in the Susquehanna River near Harrisburg, Pennsylvania. It operated from the mid-1970s until final shutdown and site restoration in the 2010s, sharing a site with Unit 2, which experienced a partial core melt in 1979. The plant's history intersects with major utilities, regulatory bodies, corporate restructurings, and national debates on nuclear safety and energy policy.

Overview

Unit 1 was built by Babcock & Wilcox for Met-Ed and later owned or operated by GPU subsidiaries, PPL, AmerGen, and Exelon. It produced about 819 megawatts electrical and served the PJM Interconnection grid, supplying power to Pennsylvania and the Mid-Atlantic States. The unit's proximity to Harrisburg, Pennsylvania and the 1979 Unit 2 accident made it central to national discussions involving the Nuclear Regulatory Commission and federal energy policy debates during administrations of Jimmy Carter and later Ronald Reagan. Corporate and regulatory decisions regarding Unit 1 involved entities such as NRC commissioners, EPA officials, and state authorities including the Pennsylvania Public Utility Commission.

Design and Specifications

Unit 1 was a four-loop pressurized water reactor supplied by Babcock & Wilcox, with a reactor pressure vessel and steam generators typical of Generation II designs of the 1960s and 1970s. The plant's design incorporated emergency core cooling systems, containment structures, and auxiliary systems influenced by licensing criteria established by the Atomic Energy Commission and later the Nuclear Regulatory Commission. Unit 1 used low-enriched uranium fuel fabricated by suppliers such as Westinghouse Electric Company contractors and refueling procedures aligned with industry standards promulgated by the INPO and the NEI. The turbine-generator was provided by manufacturers commonly used at the time, and the station's switchyard connected to regional transmission operators including Met-Ed and later PJM Interconnection.

Operational History

Construction began in the late 1960s, with commissioning during the administration of Richard Nixon and commercial operation starting in the 1970s. Unit 1 operated through the energy crises of the 1970s and into the deregulation era of the 1990s, interacting with policies under Gerald Ford and Jimmy Carter on energy. Through the 1980s and 1990s ownership changes involved GPU and the formation of AmerGen, a joint venture involving General Electric interests and PECO. Operating performance and capacity factors were reviewed by the Nuclear Regulatory Commission and evaluated by industry peer institutions such as INPO. Unit 1 underwent periodic refueling outages, maintenance campaigns, and uprate applications that paralleled efforts at similar sites like Hope Creek Generating Station and Oyster Creek Nuclear Generating Station.

Safety Incidents and Response

Although Unit 1 did not experience a core melt, the adjacent Unit 2 accident in 1979 prompted intense regulatory scrutiny of Unit 1 from the Nuclear Regulatory Commission and led to inspections informed by lessons from the Three Mile Island accident investigations, including the Kemeny Commission and federal inquiries led by John G. Kemeny. Post-1979 safety modifications referenced guidance from bodies such as INPO, recommendations by the President's Commission on the Accident at Three Mile Island, and NRC rulemakings executed under chairmen selected by presidents such as Jimmy Carter and Ronald Reagan. Emergency planning engaged local institutions including Dauphin County Emergency Management Agency and state agencies; federal coordination involved the FEMA. Unit 1 implemented procedural, instrumentation, and training upgrades, including human factors changes influenced by work from Mitre Corporation-affiliated studies and academic researchers at institutions like Massachusetts Institute of Technology.

Decommissioning and Site Restoration

Economic pressures, wholesale market conditions, and regulatory costs contributed to decisions about Unit 1's long-term operation. In the 2010s, ownership by Exelon Corporation and negotiations with state officials and stakeholders culminated in planned retirement and decommissioning actions consistent with NRC decommissioning rules. Decommissioning activities involved spent fuel management in on-site independent spent fuel storage installations (ISFSI) under NRC regulation, coordination with the U.S. Department of Energy statutory roles, and contractors experienced with dismantlement projects such as those that worked at Shoreham Nuclear Power Plant and San Onofre Nuclear Generating Station. Site restoration plans engaged the Pennsylvania Department of Environmental Protection and local governments in Dauphin County, Pennsylvania regarding land reuse and industrial redevelopment initiatives.

Environmental and Public Health Impact

Environmental monitoring by the Environmental Protection Agency and state agencies assessed radiological and non-radiological emissions from Unit 1 during operation, with public health assessments involving the CDC and state health departments. Epidemiological studies by universities and independent researchers compared cancer incidence and demographic datasets in areas including Harrisburg, Pennsylvania and surrounding counties; results informed debates involving organizations such as the National Research Council and public interest groups like Greenpeace and Natural Resources Defense Council. Groundwater, riverine ecology of the Susquehanna River, and thermal discharge impacts were evaluated against standards set by the Clean Water Act and enforced by the EPA Regional Office and the Pennsylvania Department of Environmental Protection.

Legacy and Cultural Significance

The site became emblematic in discussions about nuclear power policy, regulatory reform, and public trust, referenced in media outlets like the New York Times, Time, and documentary films that examined the Three Mile Island accident. Cultural responses included portrayals in works by writers and filmmakers who addressed energy policy debates during the administrations of Jimmy Carter and Ronald Reagan, and influenced activism by groups such as Sierra Club and Friends of the Earth. The event and Unit 1's continued operation informed educational programs at institutions such as Pennsylvania State University and prompted congressional hearings in the United States Congress that shaped subsequent legislation and NRC oversight. Museums and archives, including collections at the Harrisburg University of Science and Technology and state historical societies, preserve documentation related to the plant's technical, social, and regulatory history.

Category:Nuclear power stations in Pennsylvania Category:Energy infrastructure completed in 1974